This invention relates, generally, to airfoils and, more particularly to a closed-circuit coolable airfoil assembly of a machine.
Airfoils may be employed in various machines, for example, power turbines, compressors or aircraft engines. Vanes and blades are examples of airfoils. A blade, which blade may also be referred to as a "bucket" or "rotor," may comprise an airfoil mounted to a wheel, disk or rotor, for rotation about a shaft. In addition, a vane, which vane may be referred to as a "nozzle" or "stator," may comprise an airfoil mounted in a casing surrounding or covering the shaft about which the blade rotates. Typically, a series of blades are mounted about the wheel at a particular location along the shaft. Furthermore, a series of vanes are typically mounted upstream (relative to a general flow direction) of the series of blades, such as for maximizing efficiency of a fluid, for example, a gas flow. Such an arrangement of vanes succeeded by blades may be referred to as a "stage."
A number of stages of vanes and blades may be located in a compressor in order to compress gas, for example, to be mixed and ignited with fuel, to be delivered to an inlet of a turbine. The turbine may include a number of stages of vanes and blades in order to extract work from the ignited gas and fuel. The fuel may comprise, for example, natural gas or oil. Further, the addition of the fuel to the compressed gas may involve a contribution of energy to the combustive reaction, which may raise the temperature of the gas to, for example, 3000 to 3500 degrees Fahrenheit. The product of this combustive reaction then flows through the turbine.
In order to withstand high temperatures produced by combustion, the airfoils in the turbine need to be cooled. Insufficient cooling results in undue stress on the airfoil and over time this stress leads or contributes to fatigue and failure of the airfoil. For example, existing cooling configurations include air-cooling, open-circuit cooling, closed-circuit cooling and film-cooling, using a cooling fluid from the compressor, engine or an external source. These configurations, however, do not always enable effective cooling of the airfoil to increase engine efficiency.
Accordingly, a need exists in the art for better or improved cooling of the airfoil to increase engine efficiency.